Prevention of starch degradation in pump, paper or board making processes

Abstract

The invention relates to biocidal systems comprising zinc ions and an oxidizing or non-oxidizing biocide, their use, and methods for preventing or decreasing starch degradation in starch-containing process waters from pulp, paper or board production processes.

The invention claimed is: 
     
       1. A method of controlling starch degradation in a starch-containing process water used in pulp, paper or board production, comprising:
 treating the starch-containing process water with an amount of zinc ions and a non-oxidizing biocide effective to provide for at least a 20% decrease in the amount of starch degradation in said treated starch-containing process water relative to the same method conducted in the absence of said amount of zinc ions and non-oxidizing biocide. 
 
     
     
       2. The method of  claim 1 , wherein the zinc ions and the biocide are continuously, intermittently or alternately added to the starch-containing process water. 
     
     
       3. The method of  claim 1 , wherein the zinc ions and the biocide are added simultaneously to the starch-containing process water. 
     
     
       4. The method of  claim 1 , wherein the biocide is added prior to the addition of the zinc ions. 
     
     
       5. The method of  claim 1 , wherein the zinc ions are added prior to the addition of the biocide. 
     
     
       6. The method of  claim 1 , wherein the addition of said amount of zinc ions and non-oxidizing biocide results in a decrease in starch degradation of at least 20-40% in the treated process water, relative to a method not comprising the addition of said zinc and non-oxidizing biocide. 
     
     
       7. The method of  claim 1 , wherein addition of said amount of zinc ions and non-oxidizing biocide results in a decrease in starch degradation of at least 40-60% in the treated process water, relative to a method not comprising the addition of said zinc and non-oxidizing biocide. 
     
     
       8. The method of  claim 1 , wherein addition of said amount of zinc ions and non-oxidizing biocide results in a decrease in starch degradation of at least 60-80% in the treated process water, relative to a method not comprising the addition of said zinc and non-oxidizing biocide. 
     
     
       9. The method of  claim 1 , wherein addition of said amount of zinc ions and non-oxidizing biocide results in a decrease in starch degradation of at least 80-90% in the treated process water, relative to a method not comprising the addition of said zinc and non-oxidizing biocide. 
     
     
       10. The method of  claim 1 , wherein the starch comprises cooked starch. 
     
     
       11. The method of  claim 1 , wherein said treated process water is used in pulping of starch-containing recycled fiber and/or in re-pulping of dry broke of a paper or board machine. 
     
     
       12. The method of  claim 1 , wherein the amount of zinc ions ranges from about 0.1 to about 1000 mg/L in said process water and/or the amount of non-oxidizing biocide ranges from about 0.1 to about 1000 mg/L in said process water. 
     
     
       13. The method of  claim 1 , wherein the non-oxidizing biocide is used in an amount ranging from about 1 to 500 ppm in the starch-containing process water. 
     
     
       14. The method of  claim 1 , wherein the non-oxidizing biocide is used in an amount ranging from about 5 to 100 ppm in the starch-containing process water. 
     
     
       15. The method of  claim 1 , wherein the zinc ions and non-oxidizing biocide are added to the process water in a ratio ranging from about 1:20 to about 20:1, based on the weight of these components. 
     
     
       16. The method of  claim 1 , wherein the zinc ions and non-oxidizing biocide are added to the process water in a ratio ranging from about 1:10 to 10:1, based on the weight of these components. 
     
     
       17. The method of  claim 1 , wherein the zinc ions and non-oxidizing biocide are added to the process water in a ratio ranging from about 1:5 to 5:1, based on the weight of these components. 
     
     
       18. The method of  claim 1 , wherein the zinc ion source is selected from: ZnBr 2 , ZnCl 2 , ZnF 2 , ZnI 2 , ZnO, Zn(OH) 2 , ZnS, ZnSe, ZnTe, Zn 3 N 2 , Zn 3 P 2 , Zn 3 As 2 , Zn 3 Sb 2 , ZnO 2 , ZnH 2 , ZnC 2 , ZnCO 3 , Zn(NO 3 ) 2 , Zn(ClO 3 ) 2 , ZnSO 4 , Zn 3 (PO 4 ) 2 , ZnMoO 4 , ZnCrO 4 , Zn(AsO 2 ) 2 , Zn(AsO 4 ) 2 , Zn(O 2 CCH 3 ) 2 ), zinc metal, and a combination thereof and/or the non-oxidizing biocide is selected from glutaraldehyde, 2,2-dibromo-3-nitrilopropionamide (DBNPA), 2-bromo-2-nitropropane-1,3-diol (Bronopol), quaternary ammonium compounds (quats), carbamates, 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), 2-methyl-4-isothiazolin-3-one (MIT), 1,2-dibromo-2,4-dicyanobutane, bis(trichloromethyl)sulfone, 2-bromo-2-nitrostyrene, 4,5-dichloro-1,2-dithiol-3-one, 2-n-octyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, ortho-phthaldehyde, guanidines, biguanidines, pyrithiones, 3-iodopropynyl-N-butylcarbamate, tetrakis hydroxymethyl phosphonium sulfate (THPS), dazomet, 2-(thiocyanomethylthio) benzothiazole, methylene bisthiocyanate (MBT), and a combination thereof. 
     
     
       19. The method of  claim 1 , wherein the non-oxidizing biocide comprises glutaraldehyde.